text:
Could commercial jets take a steeper initial glide path on landing?
The context here is London. The aural environment of 9 million people (or so) is impaired significantly by the fact that we have planes landing at LHR all day long. LHR was established in the wrong location relative London, in the sense that the prevailing winds almost always blow from the West, but LHR is to the West of London. So 90% or so of landing planes overfly the inhabited city.
Instead, when East-West runways are needed, the airport should be 20 km or so from the city centre to the Northeast (like CDG), or essentially to any compass direction making it not on the East-West axis through the city.
A 3 degree slope on final may be something which can't be avoided for all I know, but might it be feasible to have, say, a 5 degree slope until the planes were a few nm/km from the touchdown point?
As a Londoner who's had no choice but to put up with this for years/decades, I have noticed that an A380's height overhead makes an immense difference to the reality of the noise nuisance and dB level experienced.
I live something like 20 km from the touchdown point (planes take a curving trajectory, before lining up more or less with Thames to the east of LHR runways), meaning that when I do the maths (the sine of 5° compared to the sine of 3°) I have no doubt this could make a lot of difference to quality of life. I'm suggesting a switch to normal 3° maybe 5 km before touchdown. According to my maths, 3° all the way gives a height of 1.05 km over me, whereas 5° until 5 km before gives a height of 1.57 km. 7° over those first 15 km followed by 3° would give a height of 2.09 km over me.
I saw this question about issues with steeper glide paths, energy management, etc.
Fuel consumption
My question is actually meant as stated: is it feasible?
Bianfable has chosen to raise the fuel consumption aspect as one reason why this would supposedly be a more environmentally detrimental approach to landing. Apart from the fact that this is not germane to my question, in fact this argument also doesn't appear to stand up: instead of descending from cruise height at a constant 3° it would be perfectly possible to descend at 2° initially, then 5° (if this is feasible, e.g. using speed brakes and landing gear), and then do the final 5 km at 3° for example.

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The simple answer to this is clearly "yes, they could". It appears that the glide path could be made steeper through the use of flaps alone. Speed brakes (or even landing gear) are obviously used to remove kinetic energy through increased drag but flaps seem to do this too. In any event there are obviously many permutations for removing kinetic energy (e.g. at higher altitudes, as discussed, before starting on the 5° slope).
I didn't ask about the fuel consumption questions. However, contrary to what is argued by Bianfable and the apparent biases of most of the commenters who have responded to this question, the issue of fuel consumption does not appear open and shut.
An interesting paper at Research Gate, entitled "On the Influences of an Increased ILS Glide Slope on Noise Impact Fuel Consumption and Landing Approach Operation" concludes as follows:

Steeper landing approaches can lead to a significant noise and fuel
reduction. Having regard to the sink rate limit of 1.000 ft/min below
1.000 ft height they can be performed only up to 4.0° glide slope angle. In addition a change of gear/flaps schedule is necessary to fly
approach angles of more or equal 3.5°, which can reduce the noise
benefit gained from the higher flight path.

Note the use of the word "significant".
Note also that this paper is concerned primarily with the whole final approach glide path (i.e. until touchdown). Part of the focus is on safety with steeper final (final-final) approaches: it concludes there isn't much of an issue with 3.5°.
My suggestion of "levelling-off" to 3° at 5 km from the runway also probably makes this concern moot. I'd be surprised if safety could be a deal-breaker with a suggested 5° until 5 km to touchdown, but ultimately don't have the expertise to say one way or the other, e.g. regarding energy management.
More research is clearly needed on the noise and fuel implications of such a two-slope or three-slope approach.

There are some issues with 3.5 deg mentioned in the paper:
"Operations in tailwind conditions on a 3.2° glide slope and a further increase to 3.5° may induce too high sink rates in piloted flight associated with the risk of a go-around."
The way I understand it, the steeper descent allows less time to correct sink rates and increases the chance of go-around.

@ROIMaison Tailwind, yes, not that surprising. Obviously certainly metereological conditions might make this sort of "composite slope" configuration less practical. In the case of LHR typically (not always) a tailwind (i.e. wind from the east) would result in a switch to "westerly operations" (planes landing from the west).

it is a bit shortsighted to only look at the descent phase when adding up fuel consumption. If speedbrakes are emploey or the gear lowered prematurely, more energy is needed which has somehow to be put into the airplane before. This could either be a longer cruise or a higher start of the descent. Either way, the fuel which seems to have beed saved during the descent phase has already been wasted before.

@PeterKämpf I don't much see the point of off-topic views based on your slavish adoration of airlines and aviation. My question is about reducing noise over London. Any money/extra fuel considerations could be cancelled out by just having fewer flights and/or making flying more expensive. LHR just shouldn't be a hub because it's in the wrong place.

If all you care about is the noise you hear, why don't you MOVE??? Is that too obvious?

Also off-topic. Please stick to the site's policy.

A descent procedure optimized to minimize noise is the Continuous Descent Arrival (CDA), where aircraft avoid leveling off during the arrival phase, which would come with increased thrust and therefore noise (and fuel consumption).

Continuous Descent Arrival (CDA) is an aircraft operating technique in which an arriving aircraft descends from an optimal position with minimum thrust and avoids level flight [...]
The objective of a CDA is to reduce aircraft noise, fuel burn and emissions by means of a continuous descent, so as to intercept the approach glidepath at an appropriate altitude for the distance to touchdown.

(SKYbrary - Continuous Descent)
The CDA profile until reaching the FAP is ideally not defined by any constraints on the procedure (STAR) nor does it use a fixed angle. It is simply based on aircraft performance1. The flight management computer (FMC) calculates the top of descent (T/D) point such that the aircraft will arrive at FAP at the correct altitude and with the correct airspeed using an idle thrust descent. A steeper angle would require less than idle thrust (not possible) or more drag (use of speedbrakes), which increases fuel consumption and is therefore not very popular2.
Your suggestion of using a 5° descent until 5km is not feasible because that is the phase where the aircraft needs to reduce its speed quite significantly. You typically slow down to 250 kt at 10,000 ft (earlier) and then to final approach speed (~150 kt) during this phase. That is impossible to do while flying a 5° descent, even with the speedbrake fully extended. It is actually more realistic to fly a steeper final approach once the extended gear and flaps add more drag, which is what London City is doing (5.5° instead of 3° final approach). While 5.5° is too steep for many airliners, 4° to 4.5° is typically possible.
Another reason why reducing noise near Heathrow is difficult, is the incredibly complicated airspace around London. There are several major international airports in close proximity with conflicting arrival and departure routes and of course a lot of congestion resulting in delays and holding patterns, which makes it difficult to impossible to implement CDA, especially during busy times.

Average holding times were about 8.5 minutes at the beginning of 2014, with that figure now just over 7.5 minutes and falling as low as 6.5 minutes in August [2016].

(NATS - Heathrow holding times on the decline thanks to new technology)

1 Modern airliners have a glide ratio of ~20:1, resulting in a descent angle of only ~2.9°. Adding idle thrust on top will only reduce this angle further. Since airliners are optimized for minimal drag in clean configuration (no flaps/slats extended), this glide ratio has been increasing over time, resulting in shallower idle-thrust-descents.
2 Any increase in drag will always result in a deviation from the optimal idle-thrust-descent and therefore result in higher fuel consumption (e.g. because a level altitude needs to be maintained longer to start the descent later or because the previous descent-segment was flown at a shallower angle).

Thanks. I don't see any justification here which might lead you to make your concluding sentence. The speed brakes and landing gear could be enlisted much earlier out to help achieve a steeper path. You say that "increased fuel consumption" is "not very popular", which is not an argument. The argument about London airspace being complicated also doesn't have any proven bearing on the question under discussion.

@mikerodent At the moment, reducing fuel consumption has a much higher priority than reducing noise for residents. This is not just true for the airlines (to save money), but also for regulators and authorities (for environmental reasons). Therefore, gear and flaps will be extended as late as possible and speedbrakes should only be used when absolutely necessary.

"A steeper angle would require less than idle thrust (not possible) or more drag (use of speedbrakes), which increases fuel consumption and is therefore not very popular.", why would deploying the speedbrakes increase fuel consumption if the engines are kept running at idle thrust?

@ROIMaison Because you would stay at cruise altitude for a longer time, therefore running the engines at higher thrust for a longer time, and then start a steeper descent.

@Bianfable, would it be necessary to stay at cruise altitude for longer? Can't you start  descent from the same point, and just use an initial shallow descent, before you proceed with the steeper descent? Perhaps that could still be more energy efficient than the stepped descent of today.

@ROIMaison Sure, you could (this is just not how modern FMCs calculate T/D), but that initial shallower descent would also use more fuel (since shallower compared to an idle-thrust-descent implies using more than idle thrust). No matter how you look at it, the idle-thrust-descent gives you minimal fuel consumption and any deviation from it will come at a fuel penalty.

@Bianfable You seem to be making a claim here which stretches credulity: you appear to be saying that, for all aircraft, at all altitudes, in all atmospheric conditions, it is precisely 3° (which coincidentally just happens to be the universal ILS gradient), which corresponds to the ideal fuel efficiency. This seems very unlikely: can you provide a link where there is some scientific proof of that notion?

@Bianfable all very well, and I'm clearly no expert in this area: but surely drag and lift are not unvarying parameters: flaps, speed brakes, landing gear, elevator trim, maybe even loading, with passengers, goods and fuel: surely these parameters must vary the L/D settings during a given phase of flight?

@mikerodent Oh yes, they sure do. Extending flaps and gear has a significant impact on L/D and therefore allows much steeper descends. Technically, you could start slowing down to final approach speed 30km from the runway, extend flaps and gear and then go for a much steeper descent (like ~4.5° to ~6.5° depending on aircraft, load, etc.), but nobody will do that due to the significant impact on fuel consumption. Also note that flying with gear and flaps extended is louder than in clean configuration, so I'm not even sure how much noise reduction this would cause.

@Bianfable Your answer still does not answer my question. Please keep politics out of this as I have been asked to do. The bolding of the phrase "nobody will do that" shows that your line of argument is fixated on following the aviation industry lines of propaganda, distortions and hypocrisy. I am asking a technical question.

@mikerodent, ideal fuel efficiency occurs when the engines aren't running.  It's inadvisable to actually shut down the engines in flight, so in practice, fuel flow is reduced to the lowest level that will keep the engines running.  For an airliner, this produces a glide angle right around 3°.  Other aircraft will have different ideal angles: a top-end glider will have a descent of less than one degree, while the Wright Flyer will come in at around 7°.

@Mark My question is not concerned with fuel consumption. However, at this point it has been established that applying speed brakes and/or extending gear would enable a steeper descent than 3° at idle. The attempts to say that despite this there is a huge fuel consumption issue involved here ("more time at cruise" etc. etc.) are clearly bad faith straw man arguments.


text:
What's the UX in modern airliner avionics for diversion choices, and does it integrate to autopilot?
This question mentions a flight that had to divert, in that case to Iqaluit (YFB).
I was wondering: in modern large airliners, what is the user interface like when diverting? How is the case of "what is the nearest airport/runway we can divert to now?" handled in the avionics displays?
Does the computer system know at all times what the nearest runway or airport is? Does that information appear when needed, or perhaps it's just continually displayed and updated at all times?
Does the system understand subtleties such as which one is best based on your current heading, altitude and so on? Or do pilots just have to quickly look up the nearest one with no special help from the avionics?
Or, is it figured out for each stage, as part of the preflight planning? Do they have it written down as part of a flight plan? Or does the crew have to program in a list of suitable diversion airports along the coming route, and if the worst happens the system will tell you which one (of that set) is nearest now?
In fact, is there just a big red button marked "Divert Now", and the plane immediately changes course to whatever it decides is the nearest and/or best diversion prospect at that moment?
To be clear, I'm talking about how it works in this sort of cockpit:

(To a civilian, most modern airplane controls look like that: touchscreens with some sort of graphical user interface.)

For more about "touchscreens", check out this question. I don't think we have a UI/UX tag as such, but "avionics" would be appropriate here.

Whether it is figured out ahead of time depends on the type of flight. For flights over populated areas (like the US or much of Europe), there is almost always a suitable alternate nearby and the pilot can just select what he feels is the best option. For flights over areas without nearby alternates (like oceanic and polar crossings), they must be selected ahead of time and exact points calculated which delineate when to divert to which alternate (for more info see Are there diversion points for southern Pacific great circle route flights?).

so awesome!  now that's how action-movie-watchers think of you guy's offices  :)

On a Boeing 777, the pilot can select to have nearby airports displayed on their navigation display (ND). It's the quickest way to get the info IMHO.
Of course this data needs to be corroborated with the nearest airport in the NavData and once a suitable airport is chosen, it can be quickly entered into the modified route - activate, execute and fly direct to.
ND showing nearby airports.
EFIS Control Panel with ARPT button to switch airport display ON/OFF.

A spectacular answer to the specific question.

This answer is so amazing, even the photos are top quality and in perfect focus!  HenryJohn, in the lower photo, is that whitish object actually a pen (or similar) with which you are showing us the button in question?  (Or is it indeed a small .. joystick or something?  It's not clear.)  Thanks!

That is a pen that I was using to show where the ARPT switch is. A MFD is a display that can have many different display configurations. It is true that while the pilot is flying, nearby airports will only show on their navigational display. This particular screen, adjacent to the primary flight display, can be selected to display a multitude of options such as synoptic information, ground maneuvering cam, central maintenance information and navigation data. This particular display in a Boeing 777 can be selected as either a MFD or ND.

thanks again for this amazingly specific answer to the precise question, cheers

There are a few options for this and it depends on the type of plane you are in, for the most part it looks like the information must at least be proactively navigated to in what ever NAV system you are using.
Every pilot should study their route before hand and identify possible diversions or at least understand where they are. For pilots flying common trans ocean routes there are some pre-arranged diversion airports that the pilot should know.
If you are using some kind of tablet as your source of navigation information (maps) most of the modern apps have a function for this.
If you have some kind of in panel GPS like a Garmin GNS system there is also a page for that very information.
According to this doc FMS systems may have this info as well. For example in the 737

This extremely useful page takes a couple of minutes to calculate but
  will list the nearest airports in the database in order of DTG.
Once again, line selection of 1R to 5R will give more useful diversion
  information as shown below.

(source)
You can also program in you alternates

You can enter up to 5 alternates here, selecting 1R to 5R against any
  entered alternate will show the info below...

(source)
The FMS will compute data to those points from the aircrafts current location.

All the diversion data is now shown based on you flying direct to this
  alternate from present position (VIA DIRECT). Selecting MISSED APP
  will show the same data but calculated from the missed approach point.
  Selecting nearest airports will give...

(source)
Even the more modern airbus cockpits contain a traditional FMS input or possibly a keyboard and mouse. To my knowledge airlines have not really adopted touch screens yet.

(source)
Some of the smaller panel avionics are starting to incorporate touch screens like Garmins GTN series however some pilots prefer the tactile feel of hard buttons.

fantastic info Dave, thanks.  fascinating, "takes a couple of minutes to calculate but will" (!) is that a typo in the manual??

The "FMS" in a 737 http://www.b737.org.uk/fmc.htm ie, this .. http://www.b737.org.uk/images/fmc.jpg (!!!!) seems amazingly old-fashioned.

@Fattie The aerospace/defense term for old-fashioned is proven.

Many of the systems may not be old inside. But a familiar interface is often kept to keep workflows efficient and tactical feel present. This caused a very large issue historically with the difference between eastern and western made attitude indicators which is why many companies strive for uniform control design even as technology progresses.

I believe on Garmin systems, the pilot can simply hit 3 buttons: "Nearest", "Direct-To", "Enter", and the flight computer will immediately show a line straight to the nearest airport.
If they configured their settings before, they can set certain parameters, such as minimum runway length, and excluding grass runways.

Gotchya.  I appreciate that on "consumer" (let's say) systems like ipads, Foreflight etc, there's such a button.  I guess I was wondering about "on new jumbo jets!" you know?  For us civilians (see image I edited in to the question), I assume the glass on a modern cockpit is one enormous touchscreen that does everything (blue button, "fly to London", yellow button "serve dinner", green button "divert somewhere with nice weather" etc) - perhaps that's just wrong.  i guess I assumed it would link right in to the autopilot?

Like the field of medicine, aerospace has a "First, do no harm" principle. As in, do not divide by zero and kill everyone on board. This means that you will probably find iphone functionality in cockpits im 20 years time. The processors in an A320 cockpit are late 1980/1990 type, the type that Apple abandoned for Intel 10 years ago. If it works, don't touch it. Even the aluminium used in the structure has a paper trail tied to it that allows for tracing for faults if required.

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text:
Is this "bearing" sentence utterly incorrect?
There is often tremendous confusion between bearing, track and similar terms.
On Wikipedia, I saw the following sentence:
NOTE CAREFULLY, THE FOLLOWING SENTENCE IS WRONG...

In aerial navigation, bearing refers to the actual compass direction
of the forward course of the aircraft.

...NOTE CAREFULLY, THAT SENTENCE IS WRONG.
PLEASE NOTE I believe that quote is totally incorrect, do not quote this page!
I refer to the "where the aircraft is going/pointing" as either "track" (the vector of motion over the ground) or "heading" (where the nose is pointing). Whereas, "bearing" means bearing regarding some distant object, (that could be either relative or absolute), and does not relate in any way to "where the aircraft is going/pointing".
{Indeed, you could just be standing somewhere - not moving and not in a vehicle - and very much talk about "bearings" to various landmarks.}
In other words, I have always thought this diagram is correct, and the only usage.
My question for actual pilots, controllers, etc, is this! ...
In fact, am I correct that the quoted sentence above is totally wrong?
Further: am I being "too dogmatic"? Hence specifically: is it the case that, in aviation, perhaps you sometimes do use "bearing" loosely to mean track or heading?
Let me repeat myself: I'm pretty sure I understand what bearing means and what track means.  But the wiki quote in question, says the opposite: in fact, is it just plain utterly 100% incorrect, a typo? Or, am I naive... ie, you dudes sometimes do use "bearing" to mean what I call track?
{Just TBTC ... for me "bearing" cannot be used about "us". The sentence "our bearing.." is meaningless.  You use bearing about another object. "What's the bearing to blah..." [Of course, that could be implicit, ie, "is our bearing still 123?" meaning, I'm still talking about bearing to Sydney as in the previous sentence...].}
As a curiosity: physics programmers (for games, whatever) constantly use these terms, and of course, we have to use them really precisely like any programming. You can imagine a character or whatever (perhaps a car in GTA!) has all these qualities, they are discussed constantly in relation to physics of the virtual objects in all senses, AI paths of tanks, etc etc.  Next time I scream at someone "that's not bearing you idiot, that's track" I want to be on a sound footing!

I've fixed Wikipedia for you. Well, only the part you refered to

Dear D-L ... I'm really pleased about that!  This site (the aviation one) is really cool, it's one of the best sites in the network.

Short answers
Here's my answers to your questions, in order:

Yes, you are correct that the quote is wrong.
Yes, you are being too dogmatic.
2(a). By the way, you are also wrong.
The quote is incorrect.  Bearing is properly used the way you describe.
I misuse words all the time, but it's not common for me (or anyone I know) to swap bearing and track.

Longer explanation
The quote isn't correct because magnetic track properly refers to the actual direction that the aircraft is moving, as read off the magnetic compass. However, you say that you refer to:

the "forward course of the aircraft" as either track or heading. (Track, vector over ground, heading, z-axis of vehicle airframe.)

Track and heading are not the same thing, and neither one is necessarily the forward course of the aircraft.  Track is the actual vector over the ground.  Heading is the direction in which the longitudinal axis of the aircraft is aligned.  Course is the correct word for the forward course of the aircraft; the intended (not actual) vector over the ground.
So you've got the definition of bearing right, but you've got track, heading, and course all mixed together.
I've been known to say "bearing" to mean "track", but it's usually only just after I've said "What be our", and just before I'm about to say "ye scurvy dog?"

(Steve: thank you so much for the answer! BTW my sentence there was slightly unclear, I will fix it!!)

"but it's not common for me (or anyone I know) to swap bearing and track" .. that is really the key info.  thanks!!  To be absolutely clear, Steve, you agree that the quote (in pink above) is, indeed, utterly, totally incorrect?

@JoeBlow Since it is a single statement, it is either correct or incorrect, asking if it is utterly, totally incorrect is meaningless. The statement you quoted is quite simply incorrect.

Simon - lol, good point  :)

Regarding the axis, there does not seem to be one standard everybody agrees on, but in the ones I've seen the longitudinal axis was called x.

@JanHudec - Me too, but since the original question used Z, that's what I kept.  Now that the original question has been edited, I suppose I could just eliminate it entirely.

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text:
Are there any current projects/plans for a VTOL passenger airliner?
I was very surprised to see there's a seemingly underway project for a VTOL "business aircraft" that seats a few people.
http://xtiaircraft.com  , https://www.startengine.com/xti-aircraft

They assert they've done a 65% scale test.
I realize historically there have been a couple military transport-sized VTOL aircraft, and there's one or two small ones today.
Is anyone contemplating a regional airliner or even full-size airliner VTOL concept?

The AugustaWestland AW609 tiltrotor is already in flight test and is being marketed for VIPs, search and rescue, and as a helicopter replacement for offshore oil rigs.

@user71659 - whoa !

!! Now with BOUNTY !!

@user71659 the AW609 is definitely an answer to this post IMO, I encourage you to write an answer giving an overview of it, since no one else has done so yet.

This is a duplicate of What are the reasons why we do not have VTOL commercial airliners? which is itself a duplicate of Can airliners benefit from vertical take-off and landing?

@zymhan The question is asking for a regional or mainline transport, 9 seats on the AW609 is too small for a regional. It would be V-22 sized and above. Talk about commercializing the Bell V-280 (a tiltrotor halfway in between the AW609 and the V-22) would be a step in that direction, but AFAIK it's been just talk.

hi @PeterKämpf !  Actually, I don't care about the reasons, nor the benefits. I'm asking Are there any current projects/plans for a VTOL airliner-size craft?

@zymhan the AW609 is an awesome small VTOL (hence the WHOA!) but not an airliner

Well, there are always some plans in some corner of every aircraft company. But for serious projects there is a massive wall of economics in the way.

US patent 9,475,585 describes a Tilt-Rotor Vertical-Lift Aircraft. This patent was awarded to Boeing on October 25, 2016. The subject aircraft may be anything from a personal aircraft to a regional commercial aircraft for at least 100 passengers.
The two tilt rotors (36) are powered by a number of turbine engines (40) which are fix mounted under the wings. The novelties claimed by this patent are about the transmission of power from the power plants (engines) to the rotors.
Figure 1 - in vertical mode:

Figure 2 - in horizontal mode:

Images source: United States Patent and Trademark Office, www.uspto.gov
Of course, the filing of a patent is an evidence that a company is spending at least some limited resources to the subject. However, this does not mean that Boeing is actually developing such an aircraft.

A fast browse of the claims suggests to me they won't be developing this to an actual aircraft. One of those things where I am not sure if it is insanely cool or just insane. Well worth a look, thanks.

Great! A jet intake located right in the prop wash! What could possibly go wrong?

@PeterKämpf, from brief reading of the text it seems that all the engines (the text says at least two) are turboshafts, attached to common shaft that drives the rotors. And the picture does not necessarily indicate actual position of the engines, so they may be either close to the tilt-rotors so they behave mostly as any other turboprop, or close to the fuselage, outside of the prop wash.

Whoa!  I wanted an example project and you brought a patent!  Unreal!

Really, I guess this is the closest thing to Are there any current projects/plans for a VTOL passenger airliner? ... thanks!

VTOL airliners were looked at in the 1960s. The Hawker Siddeley HS.141, for example:

The idea was dismissed for several reasons that still hold today:

lots of engines which use lots of fuel and are costly to buy and maintain
massive loss of payload (because of all the engines that are dead weight during most of the flight)
jet-borne VTOL is very loud (e.g. the Harrier was one of the loudest aircraft ever), and VTOL only makes sense if you can land in population centers rather than out-of-the-way airfields. so you'd run into noise regulations.

Electric motors have one big advantage over the turbines used until now: turbines are inefficient when they run at low throttle settings, so if you use one engine for takeoff and cruise, it's running inefficiently for much of the flight. Electric motor efficiency is high throughout its power range.
Whether it's viable remains to be seen, XTI hasn't published full specifications.

Electric motors may help solve the noise issue, but weight/fuel considerations remain for longer flights.

Does it essentially cost "much more fuel to take of VTOL than to take off conventionally" ... ?  Is that about right?    Is this still true with the electric motor notion?

.. and how come it's suddenly viable (unless it's BS) for a 6 seater?

@Fattie start-ups and concept designs are under no obligation to be viable.

how true, @AEhere !

Whoa - 16 lift jets !  I bet it could conveniently hovercraft around, also!  :)

Well, they're doing VTOL with first stage rocket boosters, so it may be possible at some point in the future, probably for small "air taxis" first.  The power requirements for VTOL are relatively huge, but short lived, dropping once aircraft gets moving.  Electric might do it.

VTOL with a rocket is expensive, but a lot cheaper than throwing the rocket away after 1 flight. VTOL airliners have to compete with CTOL airliners.

There probably won't be because of simple economics. (Even I can understand them, must be simple and obvious.)
Basically even a regional air liner transports a significant amount of people on a regular basis. It is not designed for single transports of single groups, it is designed to serve sustained needs. This means there must be sustained ground transport infrastructure in place at the end points for those groups of people to travel to, gather, embark, disembark, scatter and travel to their destinations.
In other words you need an airport with infrastructure to handle passenger traffic. If you have an airport, you might as well build a runway. It is basically a specialized road for aircraft and you need to build roads anyway.
If you have a runway, conventional take off and landing will be much more economical than a vertical one. That is without the extra mass of the VTOL hardware factored in. Thus the kinds of places it makes sense to use VTOL passenger craft and the kinds of places it makes sense to use air liners, even regional ones, are mutually exclusive.
The amount of traffic is either too low for service by airliners or too high for not building a proper runway that makes VTOL unnecessary waste to make sense.

Heliports are a thing. Aircraft that can transport more passengers via existing helipads should conceivably increase demand. Helicopter ferry service from Pan Am's Manhattan office tower to their airport terminal existed for a short while before an accident put a stop to the concept: https://en.wikipedia.org/wiki/MetLife_Building#Helicopter_service

@zymhan Absolutely, I am not arguing about VTOL passenger traffic just whether it makes sense to scale it to a point where you could legitimately talk about a regional airliner.

Ville, thanks for this but - I'm looking for examples of work in progress, on this question.   BTW notice there are two other questions about reasons-for VTOL (see under the question here).

Smaller airports (basically "tiny" viz a viz today) would be an tremendously major economic change, I think.  But points well made!

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text:
Why then don't aircraft fly even higher, for even greater efficiency?
After reading various superb QA on here I now see that (basically) aircraft are more efficient per passenger-mile, at higher altitudes.
Why don't we go even higher, than current typical airliner cruising altitudes?
What's the deal?
If there's an efficiency transition, have we reached it?

Really I wouldn't say it's a duplicate situation.  There are many interesting QA on the site on "the various issues of flight height" (not particularly just the one linked in the dupe suggestion).  That (particular) one (there are many others) deals with why "a certain height is good".  The excellent answers here explain "why not higher".  (Note that for example, "ceiling" is not even mentioned on the linked QA.)   I really don't think the site should close the many questions about (the many aspects of) height, efficiency, etc.

Why are you asking?

I haven't seen this mentioned, but I recall about 20 or 30 years ago that there was a period of a year or so when commercial airliners often flew at altitudes in the low 40,000s. Then they went back to the low-to-mid 30,000s.

Nobody has posted the real answer, pilots don't like to wear masks (required above 41000').  In one survey only 20% of pilots followed the "above fl350" rules.

I agree with TomMcW. The linked question has an excellet Peter Kämpf's answer (among others) explaining why airliners don't fly higher.

hi @PeteBecker , that's fascinating - any more info on that ?

@Fattie -- no, sorry. I just remember the announced altitude being 42,000 or 44,000 feet, and thinking, that's new. Then it went away.

perhaps someone will bring more info on that, @PeteBecker

@Cloud Why do you ask why he's asking?

Please meet the ceiling altitude.
Above this altitude the aircraft cannot fly fast enough to generate enough lift to stay aloft.
This is affected by:

weight (more weight needs more lift)
engine power (more lift means more drag, that is overcome by engine power)
L/D ratio (if you can have less drag for the same lift, you can fly a bit higher, all the rest being equal)

So, overall, engines are getting better, but you gain more flying a bit lower, at your ideal cruise speed, and thus consuming less.

ahh!  cannot fly fast enough to generate enough lift!   lame query, but could they just make the wings bigger, no ??   awesome info...

@Fattie as anything in engineering, there is abalance to be found. larger wings will create other problems

Comments are not for extended discussion; this conversation has been moved to chat.

@Fattie That reminds me of my second year aerospace engineering, where we had to design an aircraft. GIven the design goal was to create an ultra-long-range aircraft for medium to heavy payload, we decided to go for a higher ceiling altitude, together with high aspect ratio for more efficiency: turned out not everything is based on flight performance; when we were designing the structural components of the wingbox, the thickness of the aluminium near the root of the wings was nearly 2 cm, due to the enormous moments.

Some do (or have in the past) but very high altitudes present their own issues. Historically the Concorde cruised anywhere from FL550 to FL600 and was actually allowed to climb and descend at its discretion up there since they were well clear of any traffic. However the increase in pressure differential on the airframe as well as supersonic flight meant the airframe saw much greater wear and tear per cycle than its lower altitude friends.
At some point you get near the coffin corner a point at which, even if you have enough thrust your stall speed exceeds your critical mach number (effectively your wing can't work right). The U2 spy plane is capable of flying right on this edge.
One of the big practical limiting factors is also the rapid descent requirement for airframe certification. The FAA requires that in the event of a depressurization the aircraft can get down to 10,000 ft. (no oxygen required altitude) in 10 minutes as discussed here. The higher you go the faster the emergency descent needs to be, eventually this becomes an engineering issue and the airframe becomes the limiting factor since you don't want to exceed Vne in the dive.

and not just Vne, but G limits on the crew and passengers. While in an emergency 2G might not be too bad, once you get much higher untrained people can black out and death can occur for those with specific medical issues.

Other examples you could include are business jets like the Citation X, Bombardier Global 8000, or Gulfstream G650, all of which have a maximum operating ceiling of 51,000 ft and regularly cruise at FL400 and up.

Just want to jump in with an answer (rather than a comment) as it seems more than one answers might want to suggest that maximum ceiling on current aircraft is dictated by (available) engine power.
Flying at higher altitudes: yes, you lose density, yes, you lose a bit of lift, because of that, and yes, you will need to fly faster in order to generate that lift.  The aircraft could not care less though: That higher speed is combined with a decrease of density. Which means the wing will see the same dynamic pressure and suffer the same aerodynamic forces as on the ground.  That is why there is a difference between IAS and TAS in the first place. The same L/D ratio means you generate the same lift and the same drag (ok, almost) as at sea-level.
And while it might make a difference for a piston/prop engine, a jet engine is not delivering constant-power, but constant-thrust.  Which means engines impart the same Force on the airplane, regardless of how fast we are moving.
So where is the catch for the airplane ceiling? Compressibility.  Once you begin to acount for compressibility (which at high altitudes becomes important), IAS becomes EAS, and the wing might begin to stall even at 300 kts indicated airspeed. Climb high enough and pretty soon your wing will stall even at supersonic speeds . Maximum speed and minimum speed will meet, and you are in the dreaded coffin-corner.
Notice that the problem is almost entirely aerodynamical, and can be solved by better wings, nothing to do with engines or power.
(.. then of course, at some point your engines will stave for oxygen, making my point superfluous, but that is not why current-gen aircraft cannot fly higher at the moment)

"Notice that the problem is almost entirely aerodynamical, and can be solved by better wings, nothing to do with engines or power." this late answer seems to be one of the most insightful!  fascinating ..

You are correct in understanding that airlines primarily fly higher in order to have a more efficient flight, as there is significantly less drag due to the thinning of the atmosphere.
Explanation:
However, there are a couple issues that grow as you raise your altitude. Your wings and engines are more efficient in providing lift and thrust respectively at lower altitudes. The wings create lift via the difference in air pressure going over and underneath the wings. When you increase your altitude, your wings become less efficient because while there is less drag, you now need to increase the speed of air passing your wings in order to retain the same pressures, which then produce the same lift.
Supersonic flight (flight over Mach 1) is significantly different than subsonic flight. The air will separate from the wing when it breaks the sound barrier, and will thus cause you to lose lift. As stated in the previous paragraph, as you increase your altitude you need to increase your speed. Then, as you approach Mach 1, drag increases exponentially. The average jetliner cruises at 0.75 mach, so you can see that we are already close enough for comfort to this barrier.
The engines themselves are also reliant on air passing through them to provide thrust, and will become less efficient at higher altitudes.
In short:
In short, it really becomes a balancing act, where you have to determine if the extra altitude, and speed, is worth the drastic increase in fuel needed to power the engines to get you to an appropriate speed for your altitude. With today's technology, it is not considered cost-effective.
For comparison, the supersonic "Concorde" jet topped out at roughly 60,000 feet, while the subsonic "747" jet tops out at roughly 45,000 feet.

I feel this answer might convey a wrong picture. It's not engine limitations that prevent planes from climbing higher. While L/D remains constant (ignoring compressibility) the Lift required at 60,000 feet  is the same as the one at 100' , and drag is absolutely the same. Only once you put mach into the equation and compressibility is the drag going to be a factor.

@Radu094 I didn’t write that flying at a higher altitude would require more lift – I wrote that flying at a higher altitude requires a higher speed to retain the same amount of lift. I also didn't write that drag increases with altitude – I wrote that drag increases with speed. If you want to argue those two indisputable facts, you can call up NASA.

just playing devil's adv at the moment, but drag WILL remain constant with increasing airspeed, as long as IAS is constant. Which for our discussion it is.

I didn't say IAS, I wrote that drag increases with speed (or TAS). This was in reference to supersonic flight. You also can't "ignore" compressibility for supersonic flight.

that’s true. it’s just that the wording might have been misunderstood. And so many answers on this page seemed to suggest this aswell, I had to jump the gun.

If aeroplanes were flying significantly higher than they do today, they would be flying in the stratosphere.  Pollution in the stratosphere has a much larger global impact than in the troposphere, as pollutants stay there much longer (longer residence time).  If aeroplanes didn't have other reasons to avoid the stratosphere, environmental impact would be a very good reason to keep them out of there.
Although there is some exchange of air between the troposphere and the stratosphere, this is much less than the exchange of air within the troposphere, which happens all the time due to weather.  The European Environment Agency explains how when pollutants enter the stratosphere, they may stay there for years or even decades.  Pollutants in the lower troposphere may only remain for days or weeks.
Some decades ago, there were fears that widespread stratospheric flights would cause significant stratospheric pollution, including ozone depletion.  Since widespread aviation in the stratosphere never materialised, there are not many newer sources on the topic:

Supersonic plans threaten ozone layer, June 1990
Should flights in the stratosphere be banned?, New Scientist, April 1994
Environmental impact of stratospheric flight, National Research Council. 1975

However, one type of flight always passes through the stratosphere: space launches.  In the space flight industry, stratospheric pollution has been more specifically addressed.  For example:

Time to clear the air about launch pollution, Space News, July 2018:

Most human-generated pollution is concentrated on or near the surface of the Earth, whether on land, sea, or in the troposphere, the lowest layer of the atmosphere. However, rockets emit a variety of gases and particles directly into all levels of the stratosphere, the only industrial activity to do so. The stratosphere extends roughly from 10 to 50 kilometers above the Earth’s surface and contains the Earth’s ozone layer. The global civil aviation fleet generally cruises in the troposphere, only occasionally polluting the stratosphere directly.

For details on those processes you may want to ask at Earth Science Stack Exchange.

Whoa - this is an amazing point.  Holy crap!

PS while absolutely fantastic references - and thanks for that - they're ~30 yrs old.  Maybe someone has even newer references.  Good one.

@Fattie I've added a more recent article, albeit focussing on the space industry, it also mentions how aviation does not share this problem.

the maximum altitude for economical cruise is established by the engine technology. all air-breathing engines lose power as altitude increases, which limits the engines' capacity to maintain flight. for any given class of engine (piston, turbocharged piston, turbojet, turbofan, turboprop, etc.) there is therefore a corresponding maximum cruise altitude.

engines are only part of it. Wing design and size also are important. And as wings designed specifically for efficiency at very high altitude tend to be cumbersome low down, and quite large, they're less than optimal for airliners.


text:
Can private pilots run other non-passenger flight businesses?
As I understand it, private pilots can not take paying passengers.
(Friends on a flight can give the pilot strictly only the friend's share of fuel etc. costs.)
But in fact can private pilots

do aerial photography/videography and charge for it?
do reconnaissance/similar and charge for it?
deliver packages, or indeed cargo?
drop skydivers for pay
pull up gliders for pay

What's the deal on that?

As with any regulation question, this may differ per jurisdiction.  Also, sorry if it'd a dupe already...

Since it can, and probably does, vary with jurisdiction, it would help if you specified one.

The fact that the OP has now received two answers which state the exact opposite thing for the same jurisdiction underlines why so many Stack Exchange sites have a strict "no legal questions, ask your lawyer" policy.

hi @JörgWMittag , it's not a legal question.  It's a question about PPLs (there are a large number of PPL questions on here - it even has a tag!)

There is a YouTube pilot, PilotBambi, who flew planes dropping skydivers in the Netherlands with a private pilot certificate. Jurisdiction matters, but definitely not allowed in the US.

@Fattie I did more research on this in reaction to your question about who the lawyer that wrote the white LOI was.  My answer has changed.

@Fattie: How do the answers differ? They agree on every point...

hi @AaronHolmes !  Ah, notice the history of edits :)

@Fattie: Oh, I see. I gave the right answer first, then someone posted behind me with inaccurate and out-of-date information. Then they changed it several times until it said exactly what I was saying from the start, except with more legal tangents thrown in. And now, they have twice as many upvotes... Stack Exchange is so much fun!

In the U.S. the answer to most of these questions is a resounding “No”.

No aerial photography.
No aerial survey or reconnaissance
No cargo or property delivery
No skydivers (they count as passengers, after all)
Yes for glider towing.

Oddly, according to FAR §61.113(g), glider towing is one very specific exception in which private pilots may receive compensation or hire for acting as PIC.

According to the current FAA stance on the issue, none of it is allowed except glider towing.
The latest interpretation from the FAA that I'm aware of is the 2010 Perry interpretation, however, there was a conflicting letter (Del Rossi) from 1987 that said the opposite from the White interpretation.  The FAA further clarified the discrepancy between these two letters in 2010 with the Perry interpretation. (Note: this link contains both of those interpretations from 1987 and 2010 together.)
The FAA acknowledged the discrepancy in 2010 and determined that the older letter took precedence because it was issued by the national office, but the White interpretation was issued by a regional office, although on a later date.
For aerial photography and survey, if it is in furtherance of their own business and is simply incidental to that business, yes, they may perform the work as a private pilot according to the White interpretation.  The other interpretations, which take precedence say this is wrong.
If someone else hires them to fly so the passenger may do those things, it's definitely not allowed nor has it ever been mistakenly indicated as allowed by the FAA for private pilots in past interpretations.
There is the White interpretation from 1995 that incorrectly states:

To the extent that your operation would be in furtherance of your own
business of aerial photography or survey, and you are not carrying
persons or property for compensation or hire, then you may do so
holding a private pilot certificate. However, to the extent that your
operation would involve operating your aircraft as an aerial platform
for other photographers, etc., for compensation or hire, you would
need to be the holder of at least a commercial pilot certificate in
order to act as the pilot.

So, in short:

Do aerial photography/videography and charge for it? - No, but it was mistakenly allowed according to the White interpretation in 1995.

Do reconnaissance/similar and charge for it (aerial survey)? - No, but it was mistakenly allowed according to the White interpretation in 1995.

Deliver packages, or indeed cargo? - No, this would be carrying property for compensation or hire. See 61.113(a)

Drop skydivers - No, this would be carrying passengers for compensation or hire. See 61.113(a)

Pull up gliders for pay - Yes. See 61.113(G)

If you're actually planning on flying and making money somehow related to that flying and you aren't 100% sure you are legal, please ask an aviation lawyer in addition to online research.
If even the FAA managed to make a mistake on the subject, there's plenty of room for the rest of us to do so.

thanks - the White Interpretation ... who or what is "Leland S. Edwards, Jr. Attorney".  An FAA personage?  Just some attorney ?!  I see it seems to come from https://www.faa.gov/about/office_org/headquarters_offices/agc/practice_areas/regulations/interpretations/  (perhaps this is familiar to aviators, but not me ??)

Answer is updated based on new information.


text:
What does 3Q8 mean in the aircraft model Boeing 767-3Q8?
I have aircraft types like Boeing 767-3Q8, Boeing 767-33A, Boeing 767-3P6ER and many others. I know what ER means. But what is coded as 3Q, 33A, 3P6 etc.?
How can I convert it back to more common types like Boeing 767-300? Just replace last two symbols with 00?

Those are Boeing's customer codes. They denote which airline the aircraft was originally built for, not necessarily the airline that owns/operates the aircraft currently. For example, Southwest's customer code is H4 but they operate some 737-7BD's, which are from the AirTran acquisition. In your case, the Q8 means it was originally built for ILFC, a leasing corporation.  A full list is available here:
http://en.wikipedia.org/wiki/List_of_Boeing_customer_codes
Your assumption about replacing the customer code with 0s to get the plain old model is correct.

Technically the code indicates a customer configuration, rather than a customer. E.g. KLM took delivery of several 737-8K2 and -9K2 models (Transavia customer code) that were ordered in a single batch with Transavia's own (Transavia got 737-7K2 and -8K2 models, no -9K2).

As an aside, it is interesting to note that on the 787 it seems that Boeing has decided not to include the customer code at all and simply denote the model as '787-8' (for example) source


text:
Are there any aircraft with powered landing gear?
My student asked me a question this morning.  It was:

A car drives by turning its wheels against the Earth. An airplane taxis by rolling on its wheels while the engines push against the air.  Are there any airplanes that taxi by turning their wheels, like a car?

I assume the answer is no for reasons of weight, complexity, and so on, but it's dangerous to say never.  Are there in fact any airplanes that fit her description?
Edits in response to comments:

She was thinking of "normal" airplanes, not airplane/car hybrids.
Peter Kämpf's link is the kind of thing she was thinking of.

Well there's this :D https://www.youtube.com/watch?v=0Yn2uyQJ1jc

Very related: What is the cost savings of using electronic motors to taxi?

This one can or at least will be able to once somebody makes it.

The Aerocar? But I suspect your student is asking about a 'normal' aircraft that has powered landing gear, not a 'flying car'. Is that right?

the Glowfly is in development: http://www.proairsport.com/project-glow.php . Uses powered wheels to get up to 45mph, at which point the turbojet can take over.

Hang gliders and paragliders could be said to have powered landing gear, just not involving wheels!

WheelTug makes an addon motor for a nose wheel. This is a demo of the unit being developed for a B737. They intend to lease it to airlines. It works well under most circumstances, but has difficulty on icy aprons where the aircraft would need a pushback so it could taxi using its engines. The terms of the lease would financially compensate. They have "reservations" for 1100 units from two dozen airlines.

youtube
There are a number of financial considerations, such as cost to carry the weight of the unit. Here is a presentation of their business case. They claim direct cost savings similar in value to installation of winglets, and time savings value twice as great as replacing a current generation 737/320 with a Max/Neo.

youtube
Safran also had a joint venture to develop a similar unit for aircraft maingear, but that is no longer being pursued. I don't know of any OEM that offers this kind of capability on commercial aircraft. Here is the Safran/Honeywell solution.

youtube

Oh? Didn't know safran green taxiing solution was abandoned!

@le_daim The joint venture was abandoned when fuel prices dropped. Safran kept some research activity going and they may try again with different partners. Their maingear approach required two units instead of a single at nose and was quite a bit heavier, though it was less vulnerable to ice. There may have been some market acceptance problem.


text:
Is it possible to do linear interpolation on a manual E6-b?
Suppose the performance tables for my fictional airplane indicate the following:
    Density             Takeoff
  Altitude (ft)       Distance (ft)
----------------    ----------------
       0                 1,865
      2,000              2,602

Suppose that the density altitude of the day is 1,400 ft and I would like to calculate my takeoff distance.  Obviously I could do it using the linear interpolation equation:
\begin{align}
y &= \frac{(x-x_0)(y_1 - y_0)}{x_1-x_0} + y_0 \\
&= \frac{(1400-0)(2602 - 1865)}{2000-0} + 1865 \\
y &= 2,381 ft
\end{align}
...but that's a lot of numbers.  I suppose some digital E6-b's might have a linear interpolation solver, but is there a clever way to calculate (or estimate) it using a manual E6-b?

Edit:  To be explicit, I could not care less about actual takeoff performance for the purposes of this question.  It's just there so we have a common example to use when discussing the actual question of E6-b manipulation.

Why not just use the next number up? 2,381 feet is only 221 feet shorter than the next number up, if you are taking off where 221 feet means the difference between "skyward" and "in the fence", please don't fly. The performance numbers were generated with a great running aircraft with a test pilot at the controls.

@RonBeyer - Because the question isn't actually about takeoff performance, it's about E6-b use.  I could change the example to be a table of antelope in the savanna exhibiting linear growth and the title question would remain the same.  I may not have made that clear enough, so I've edited the question.  Thank you!

My advice in this case would probably be: Once you know the density altitude, don't bother with the flight computer. The exact values are going to depend enough on the specific airplane that a general-purpose device will only get you approximations anyway, no matter what you do.
Rather, consider that for your fictious case, when going from a density altitude of 0 feet to 2,000 feet, takeoff distance increases from 1,865 feet to 2,602 feet.
Split the difference into reasonable, approximately equal-sized chunks. Say density altitude 0 ft, 700 ft, 1,400 ft, 2,000 ft. Calculate take-off distance for those, possibly based on a linear extrapolation (which isn't going to be exact), and note the change in take-off distance per change in density altitude. In your example case, for every 700 ft of density altitude increase in this range, the take-off distance increases by about 250 ft. Alternatively, for every 1,000 ft of density altitude increase in this range, take-off distance increases by about 370 ft. (If you're in a metric country, this happens to work out nicely to a little over 100 meters of runway per 1,000 ft of density altitude increase, so for a first order approximation you could just cross over the final digit in the density altitude in feet.) Note these values.
Now suppose that the density altitude for your airport of choice on the day and time of your flight is 1,370 ft. That's reasonably close to 2,000 ft minus 700 ft, so take the take-off distance for 2,000 ft (2,600 ft, give or take) and subtract 250 ft to get an approximate value of 2,350 ft take-off distance for this density altitude.
Or suppose the density altitude is 491 ft. That's closer to 700 ft than it is to 0 ft, so take the take-off distance for 0 ft (1,865 ft) and add 250 ft. That gives about 2,100 ft take-off distance. If you split into thousands, you could take half of 370 ft or about 200 ft, for a hair over 2,050 ft take-off distance.
For your example case, if the last hundred-ish or so feet of runway are going to be what makes or breaks the take-off, then I suspect you're cutting it too close anyway, so this level of accuracy should be sufficient for general aviation. With this, I'd probably have a rule of my own saying that if the runway length is less than, say, 150% of the calculated take-off distance, it needs a more accurate calculation or manufacturer performance data lookup; if the runway is less than 125% of the take-off distance thus obtained, it's a no-go. Remember that you have to be able to safely abort the takeoff even late during the takeoff roll!


text:
What was used instead of the failed engine when ferrying the Air France Flight 66 aircraft back?
After engine 4 failed in Air France Flight 66, the airliner (an Airbus 380) landed at Goose Bay in Canada. I am aware that following that, the failed engine was removed and then something "nonfunctional" was installed in its place "to balance the weight". This looks like a strange story to me:

What was this "non-working replacement" and where did they get it? It still needs to have the required weight, shape and mountings. Was it quickly manufactured? The source referenced by Wikipedia even calls it a "spare engine". Did they install the engine intended for a different airliner?
In general if the goal was just to have a non-operational engine on the wing, why not leave the failed no. 4 engine where it was? Or was there a risk of it falling to pieces during the ferry flight?

Something like this? https://aviation.stackexchange.com/questions/43117/why-are-empty-pylons-weighed-down#comment110820_43117

To most Canadians, Goose Bay doesn't really qualify as the "Far North";  that term is usually reserved for places north of 60°N.  And aircraft do sometimes have to divert to the Far North of Canada.

To emphasize what Michael says, I have friends who grew up and still have family living 2000km north of Goose Bay.

https://en.wikipedia.org/wiki/Air_France_Flight_66

In Wikipedia, it is only written " non-working replacement fitted".

Nothing. As of today, the ferry has not taken place.

Here's another article from Oct 15th. They flew out a spare A380 engine. As of the 15th, it wasn't clear yet if this engine will be connected and running during the flight, or if it'll just be there to complete the airframe and act as a counterweight.
Leaving the broken engine in place would do more damage to the engine, complicating the investigation.
Pieces breaking off from the engine may have damaged the wing, the pylon or the connectors on the pylon (power, fuel, electronics etc.), they need to inspect for damage before deciding if the spare engine can be connected and running.
The plane will be empty for the recovery flight, so there's some margin to fly on 3 engines. They have to account for the possibility of an engine failure, leaving 2 operational engines, so the flight is planned to ETOPS rules.
There's a procedure to reduce the effects of asymmetric thrust.
If the engine is left off and windmilling, it needs lubrication, this may limit the length of the flight.

"so there's some margin if they want to fly on 3 engines." In fact, B747s with a failed engine usually take off on recovery flights with only 2 engines running at max thrust and the other at idle, to minimize the issues at the list-off point where the wheels no longer help to control unsymmetric thrust distribution - this is the reverse of a "landing in a very strong cross wind" scenario except that gravity is working against you, not for you!

The engine/aircraft connectors are often mounted on the fan case (because it's the closest point to the pylon and wing, and also the coolest part of the engine), so it's very likely the aircraft side of them would be damaged when the fan "fell off", irrespective of any other damage to the wing.

Capt Dave Wallsworth is a British A380 pilot, and has some good info about this in his twitter feed. See https://mobile.twitter.com/DaveWallsworth/status/917887041278566400

@alephzero Your statement that B747s with a failed engine usually take off on recovery flights with only 2 engines running at max thrust and the other at idle" is not quite correct. The procedure, at least on 747-100/200 aircraft, is to start the aircraft rolling with max power on the symmetric engines, idle power on the other. Then as the aircraft gains speed and the rudder gains authority, the third engine is brought to max power. You have full power on all three engines well before rotation.

fixed my answer, thanks

The plane returned with all engines operating normally on December 6th.


text:
How common is it to take off from a taxiway?
This question reminded me of a time when I landed my spamcan at a former WWII RAF base (middle of nowhere, no ATC, no-one in the clubhouse) that had a part concrete/part grass runway, a farmer came out to mow the grass runway and advised that, if I wanted to take-off, I could use the taxiway.  I wimped out and waited till he'd done and used the traditional method.
I was wondering how unusual it is to take-off from a taxiway when it's legal and feasible?

I know at some high-traffic airshows, they will open taxiways for use as runways for GA aircraft.

It's less common than taxiing on a runway...

At an uncontrolled airport, where you take off is up to you, the airport owner and your insurance company. There's nothing stopping you from taking off from any surface, as long as you respect government regulations against causing a danger to others (say your taxiway departure scares somebody and they complain), the wishes or policies of the airport manager or owner who implicitly grants you permission to use the facility, or your insurance company's policies on use of unlicensed surfaces.
As far as the regs go, generally the pilot's decision to use a particular surface is deemed to designate that surface an "aerodrome". But use of taxiways is rarely done because it's simply bad etiquette and there's a better surface nearby, so it would be pretty rare outside special circumstances.
On the other hand, in winter in North America, you will have ski planes using areas off the runway, usually parallel to it, to operate from, maybe on the opposite side to a taxiway.
Your actions were perfectly reasonable, but myself as an ex bush pilot used to operating off-airport (lakes mostly) I'd have used the taxiway if there was nobody else around.

then again, when Meigs field was illegally demolished by the mayor of Chicago it took a special decree by the FAA to allow the trapped aircraft there to take off from its taxiway, despite there being no usable runway left at all.

@jwenting Meigs also had an FAA control tower.


text:
What VFR cruising altitude should be flown to the west below 4500 feet?
This is similar question to this question, but different scenario.
Let me describe the situation:
I am at KDYL in class G airspace. Accroding to ATIS the clouds are at 4700 scattered. I am going to fly west. I would like to fly below clouds. I will need to have 500 feet clearance below clouds in class E, so it is going to be 4200.
Do I have to comply 91.159? What altitude should I fly? Can I fly 3500 west in my scenario or I have to descend below 3000 and fly any comfortable and safe altitude?

Note that the ASOS (not ATIS) will report ceilings in feet AGL, not MSL, and note that DYL is at an elevation of 400 MSL. Thus a report calling "ceiling 4700" means the ceiling is 5100 MSL; flying at 4500 MSL will provide sufficient cloud clearance.

Yes, you would have to comply with §§91.159.  If you’re flying VFR westbound (180°-359° magnetic) at >3000 ft AGL,  you will need to fly at even thousands + 500 ft, except while in a holding pattern or turning.  For a forecast of scattered clouds, you will simply deviate from your course for cloud avoidance, then return to the route.

Can I descend to avoid clouds below 3000 ft to comply 91.159 and fly there for some time and then return to the route at 4500 when it is clear?

You can descend below 3000 ft AGL, and fly the route.  But if that’s not possible for terrain or obstacle avoidance, you will have to maintain altitude and divert course or climb to an altitude which provides a VFR cloud clearance and fly there.

Flying AT 3000ft (which 3k MSL is probably always below 3k AGL) is also allowed but people fly that altitude and below in both directions so keep your eyes peeled. TCAS/TIS and talking to ATC recommended also.


text:
A question on stalling and flat spin - in gliders
Very short version: Do gliders do stalls, and flat spins, as aerobatic tricks (as do say aerobatic biplanes).
--
As I understand it, with an aerobatic plane, a pilot can and does, for "fun" as it were, and for training purposes, and as part of certain (?) aerobatic trick displays, deliberately stall the craft (is that the correct way to put it?) and indeed subsequently (as I understand it) put the craft in to a "flat spin" (which I guess can be looked on as either a "particularly good-looking trick from the ground" and/or a death situation). And indeed then can recover from that (by doing something tricky, I believe along the lines of waiting a breathtaking amount of time, stomping on one pedal one way and slamming another lever another way). As I further understand it, indeed for pilots in (advanced? aerobatic only?) training, deliberately stalling (and obviously recovering) is part of the training. (But maybe that's wrong, and/or only applied in the past.)
My question is simple, does the same apply with gliders?
Can/do you deliberately (ie, as part of an aerobatic trick or display) stall gliders? Or is it just not a thing with gliders?
(I suppose associated questions to clear up my misunderstanding; in general does a stall always result in a "flat spin"; I believe there's a thing where you point the plane straight up until it basically tumbles - can you do that in a glider and is that indeed the only way to "stall a plane deliberately to perform a trick" or are there other ways; beyond gliders can All aircraft be stalled deliberately and then recovered - or is that say plain impossible in a plain old Cessna (you'll die) but possible in a "Pitts special" type acrobatic plane, ie the Pitts is literally designed for that purpose, to recover from a stall? flat spin? whereas in a Cessna it's death - ?)
I guess a thrilling addendum would be, has anyone on here stalled a glider!  TY

Some practical advice about intentionally (nearly) stalling a glider.  It's not so much thrilling as just the stick feeling mushy and the wind getting too quiet.

In Canada spins are part of basic flight training in both gliders and power planes. If the airplane is not certified for spins, an "incipient spin" is sufficient, where you enter and recover right away so that it goes no more than 1/4 to 1/2 turn.  Airplanes with a flat spin tendency usually take several turns for the nose to come up and become flat,  so incipients are not considered dangerous on aircraft not certified for spins. In the US the philosophy, in power flying, is spin avoidance, not spin mastery, and they have not been taught as a mandatory part of the curriculum since the 70s.

Yay Canada!  Seems much more sensible to me. If only Richard Bach was on this list to rant about the issue  :)

Has anyone EVER put the modern generation of airliners actually in to a flat spin or two, to see how all the simulations play out in real life? Is there perhaps some badass test pilot or such out there who would answer "Sure, I put my A380 in to flat spins all the time..."

All aircraft, in fact anything with a wing, can stall that wing. A stall is simply the increase of angle of attack beyond a specific point.
Not all stalls result in a spin. In fact, for the purpose of flight training, the stall characteristics of a simple trainer, like a Cessna, are demonstrated and practiced repeatedly. The process for recovery is simple; at the onset of the stall - characterized by buffeting and lack of aileron control usually - the control yoke/stick is pushed forward to lower the nose (and by extension AoA) and throttle is increased to recover airspeed. You can often go beyond this and recover a fully-developed stall which is often characterized by the sounding  of the stall warning horn. The recovery from this is similar.
When you fully develop a stall, and even go beyond, there is every opportunity for one wing to stall before the other - this happens if your are not in coordinated flight (ie, you're yawing). If one wing stalls before the other you may well end up with that wing dropping, which left unchecked will result in a spin. You can also force this situation by stalling the aircraft and pushing the rudder one way or the other - this is how you initiate a spin for the purpose of inducing a spin.
So why would you do that? It used to be a standard part of flight training - to recover a spin - it no longer is in most jurisdictions because (rightly or wrongly) it was deemed that the dangers posed by practicing it outweighed the benefits.
I, like many pilots, wanted to practice it in case I ever did find myself in a bad situation. So aerobatics training organisations will provide training.
The process is fairly simple (albeit vary slightly by type); In a spin your wings are stalled, so the ailerons have little or no affect. Center the ailerons and, somewhat counter-intuitively you want a bit of forward pressure and to cut the throttle to stop you over-speeding. Use rudder in the opposite direction to the spin (ie, a clockwise spin requires left rudder) to break the spin. This will then see you pointing down, but wings somewhat level. At this point you recover from the dive using elevators, but not too quickly as to over-stress the airframe. Easy, but disorienting if you've not done it before. Recovery from a flat spin has some slightly different steps, but for an experienced aerobatic pilot I'm led to believe not all that bad.

Incredible.  TY.  Just two points then from the Q, in a glider: do you practice stalling it in the "simple" sense (as you describe happens learning a Cessna); and in a glider is it actually possible to (deliberately, for trick purposes) put it in to a spin (or is that impossible, it would just break up or something and/or be non-recoverable).  (Also just TBC is "flat spin" the correct/OK terminology for what you describe in para 3 ?)

@Fattie I have a very limited experience in gliders, but I suspect they practice stall recovery moreso than powered pilots. Some aircraft are almost un-stallable when they reach critical angle of attack rather than pitching nose down they just descend with a high AoA - but other than that anything can be stalled glider or powered. A flat spin is a specific type of spin, i'd suggest looking up the details but it certainly is a known type of spin.

Some airplanes can't stall because the elevator's too weak to pitch the nose up far enough.  Although even then, you might stall it by shoving cargo way aft of the allowable CG range.

A spin is a quasistationary state in which the plane rapidly spins around a vertical axis, driven by lift differences between its wings. The spin axis is located close to the nose of the airplane, so its tail and wings swing around. This induces additional speeds on them, increasing the local angle of attack on the receding wing and vice versa on the progressing wing. While the receding wing shows fully separated flow, part of the progressing wing experiences attached flow.

Principle of a regular spin (picture source)
In a regular (steep) spin the angle of attack at the center is between 30° and 60°, and the control surfaces keep some of their effectiveness. A flat spin occurs with an angle of attack well above 60°, so all flight surfaces and their control surfaces show fully separated flow.
Of course you can stall gliders. However, putting them deliberately into a flat spin is rather impossible without specific modifications to them. Part of the certification tests is to enter a spin and prove that this is either impossible or easy to end. Flat spins are very hard to end, so a glider which gets easily into a flat spin will not be certified.
How a flat spin develops and what preconditions must exist for it to be possible is explained here.
When I talk of spins from here on, I mean regular steep spins.
The normal way for entering a spin is to slow down and stall, then kick the rudder hard in one direction. The airplane will yaw and roll and pretty soon enter a spin or a spiral dive.
Some gliders will not enter a spin but only a spiral dive. Due to the much lower drag in a spiral dive, speed will quickly increase and will make this maneuver very dangerous if the dive is not ended soon. For example, the popular training glider ASK-21 will not spin if flown by two people. Flown solo by a light person, it will happily spin and the spin can be ended already if that person unbuckles and leans forward. The small shift in the center of gravity will be enough to end the spin.
In glider aerobatics spins and inverted spins are performed routinely. Inverted spins are started in inverted flight, but otherwise in the same way as upright spins. It is advised, however, to pull out of the spin into upright flight instead of ending the spin inverted. Multiple negative gs are painful!

Thank you so much.  Sorry, one thing not clear:  "In glider aerobatics spins and inverted spins are performed routinely."  In that sentence, what is meant by "spin"? (I understood the bulk of your answer to explain that: "gliders generally can not do a flat spin".)  Is the explanation that: in your 3e para, should I read that as "spin" is aka "spiral dive" ..?  And what is an inverted spin? (Sounds terrifying!)

Am i correct in guessing that something like this .. https://pilotinstitute.com/stall-turn-hammerhead-explained/ .. is totally impossible in a glider?  :O

@Fattie A hammerhead turn (in German: Immelmann) is possible with a bit of entry speed and actually a lot of fun in a glider.


text:
What's the plug used on airliners for ground power?

What's the plug pair called?
What's the ISO/whatever standard involved?
What do they look like close-up?
Is it pretty standard today worldwide?
Is the plug identical for the hugest airliners as for say commuters?
Is the power specs identical for the hugest airliners as for say commuters?
Is the plugpair used on any non-aviation (say, industrial) cases?
Do some craft have more than one type of plughole (ie, to allow for different airport standards?)
And military aircraft?
Do any small personal craft (I mean 2-4 seater craft) use the same plugpair, or in some cases do they just use a domestic-like plug (rather as a motorhome may have), or generally do small craft never have this?

 (found a pic but not a close up of the plug/hole!)

Is there a switch (for example, perhaps near the pylon in the first photo?), or a switch near the plug, or does it just hot connect?

When you say "small private plane", do you mean a small biz-jet or something smaller like a 172? I know on my 177 there is an external plug but it is primarily for jump-starting and charging, accessing it is behind a screwed down cover on the tail of the aircraft.

Possible duplicate of What is the cable connected to a plane for?

It's not a duplicate.

@RonBeyer thanks, i clarified

@Hobbes , I might say it's surprising you marked that as a duplicate!

Ah, I see how you're reading it !!   note that I'm literally asking >>> about the plug <<< , what's the format, name, standard, etc of the plug pair.

It is a duplicate. From the linked answer: "These connectors are standard for all aircraft, as defined in ISO 6858."

What's the plug pair called?

I don't think there's an "official" name for it, but it's usually referred to as the "ground power connection" or something similar. Also, there's usually only one connection; only the biggest commercial aircraft need two connections simply because one connection can't supply enough power.

What's the ISO/whatever standard involved?

ISO 6858

What do they look like close-up?

I wasn't able to find a copyright-free picture, but here's a PDF catalog from an aircraft parts supplier that has some pictures. (Note that this catalog also has a bunch of rarer plugs in addition to the common ones.)

Is it pretty standard today worldwide?

The international nature of aviation kind of militates towards better standardization than most other fields. It's not perfect, but you're a lot more likely to find a compatible plug for your plane in a foreign country than you are for, say, your electric razor.

Is the plug identical for the hugest airliners as for say commuters?
  Is the power specs identical for the hugest airliners as for say commuters?

The plug is based on what kind of power the airplane needs, rather than the size. So, all airplanes that take 120V 400Hz power will (usually, see above about standardization) have the same plug.

Is the plugpair used on any non-aviation (say, industrial) cases?

No, not that I know of.

Do some craft have more than one type of plughole (ie, to allow for different airport standards?)

It's a pretty big world, so I'm sure that some airplane, somewhere, has multiple plugs.

And military aircraft?

That I don't know. Someone else will have to answer that one.

Do any small personal craft (I mean 2-4 seater craft) use the same plugpair, or in some cases do they just use a domestic-like plug (rather as a motorhome may have), or generally do small craft never have this?

Generally, most small aircraft use 28V DC power, the connector for which can be found in the catalog I linked to.

Is there a switch (for example, perhaps near the pylon in the first photo?), or a switch near the plug, or does it just hot connect?

Generally, the switch is in the cockpit rather than next to the plug, and it's the pilot's job to make sure there's no hot connect/disconnect.

WOW. it's like a six-hole thingy.  I've used an awful lot of industrial power plugs but never seen one like that !

Some aircraft have an AC GPU connection and a separate DC GPU connection.

"Generally, the switch is in the cockpit rather than next to the plug", there is indeed a switch and a security on the cable plug, to prevent hot disconnect at currents about of hundreds of amperes. See: What is the process to disconnect ground electric power before pushback?


text:
How does a commercial flight pilot handle turbulence?
In general, passengers dislike turbulence. Avoiding all turbulence sometimes is not viable, as it would make the flight too long, too expensive (fuel consumed), or simply not having alternatives.
How does the pilot deal with turbulence? Does he or she keep the same altitude? The same speed (relative to the wind)? Increase power?  AoA?

Most of the time the turbulence we experience is termed "chop", which is akin to what you experience on a boat on the lake -- bumps but no real altitude deviations.  With altitude deviations we'll call it "turbulence".  Within these broad categories we'll qualify them with "light", "moderate", "severe" and "extreme" in reports to ATC and other aircraft.  These reports do suffer from a fair bit of subjectivity with respect to aircraft type (wing stiffness) and pilot experience.
If it is light chop, I'll generally just ride it out and turn the seatbelt signs on.
The first thing I'll do if encountering moderate chop or turbulence is to query ATC and get ride reports from aircraft ahead of us and at different altitudes than us.  From this information I'll make a determination to ride it out or to request a climb/descent.  If the turbulence was particularly bad, slowing down was an option, but I only came across that need a few times.  Our ability to descend would often be limited by route length and fuel and major lateral deviations also depended on contingency fuel, so in some cases we had no choice but to stay in the chop.  If the turbulent areas were well forecast or had lots of PIREPS, our dispatchers would sometimes route us differently.
As for power adjustments, if we weren't slowing down due to aircraft limitations I would just adjust power so that maximum airspeed deviations stayed below Mmo.

Some large aircraft (maybe all?) have a minimum and maximum turbulence penetration speed. For the 747-100 and -200 aircraft the minimum was 270 knots and the maximum 320 knots IAS. I forget the mach equivalents.
Those same aircraft had a turbulence mode on the autopilot that reduced the sensitivity to pitch and roll deviations. However, many pilots (including myself) would hand fly through heavy turbulence because the autopilot ride even in turbulence mode was worse than what we could get by hand.
There are situations in which changing altitude is not an option. For example, if you cannot descend because doing so would burn too much fuel, but you cannot climb because you are already as high as you can go. It also may not be possible to deviate much from your course because of fuel considerations.
Consider a Hajj flight from Jakarta to Jeddah. It's 10 hours and that's what you've got fuel for. Depending on the time of day, there is often (seemingly always) a line of thunderstorms too long to go around between Sumatra and India. You pick your way through the line using radar to avoid the intense echoes.

The pilot can slow down the plane, or he can try flying at a different altitude. He also has the option of flying around it, although many times this is impractical.


text:
Do some helicopters require classes, type ratings, or special endorsements, the way some airplanes do?
I've been looking online for the different ratings and classes of helicopters but I can't find much.
For example in fixed wing aircraft you have retractable gear, constant speed propeller, IFR, multi-engine, tricycle gear, etc.
I am curious to know what the helicopter equivalents are. What does a basic helicopter rating allow you to fly? What comes after that?

I attempted to make the title of your question more clear, but if I misunderstood your intent, please feel free to revert it.

@SteveV. no problem, thanks for the clarification!

Are you asking in the context of FAA regulations?

@JonathanWalters an FAA regulation would be great if you have one

I can't see a connection between "classes" of helicopters and ratings.
You also don't specify which jurisdiction so I will answer for the UK CAA which I know.
To fly any helicopter under VFR needs nothing more than your license, gained on any type, and a type rating for the specific aircraft.
For example, I gained my license on the R22.  I am therefore also type rated on it.  The second aircraft I learned to fly was the B206 which is jet powered.  I didn't need anything extra than the appropriate type rating.
I can fly any helicopter for which I am rated under VFR.  If I had an IFR certification, I could fly any helicopter I am rated for under VFR, and any IFR certified helicopter for which I am rated under IFR.
"Difference training" is simply part of the the type rating.  For example, if I ever learned to fly a craft with a retractable undercarriage, I would be rated to fly that type, but not another type with retractable gear.
What does differ is the type of license, e.g. CPL or ATP.  I would need that license in order to carry passengers for hire and to conduct other commercial operations, but I still need a type rating on whatever helicopter I use to carry those passengers.
Put it this way, the day after I gained my license, I could climb into any helicopter and act as pilot under training.
Hope that's all clear!

Note: This answer is given for faa-regulations

Short Answer:
Rotorcraft is an aircraft category; helicopter and gyrocopter are classes of the rotorcraft category.
Longer Answer:
14 CFR 1.1 defines aircraft Categories and Classes for airman certification, and gives examples of each. In these definitions helicopter is included under classes; rotorcraft is included under categories.
14 CFR 1.1, Category:

Category:
(1) As used with respect to the certification, ratings, privileges, and limitations of airmen, means a broad classification of aircraft. Examples include: airplane; rotorcraft; glider; and lighter-than-air;

14 CFR 1.1, Class:

Class:
(1) As used with respect to the certification, ratings, privileges, and limitations of airmen, means a classification of aircraft within a category having similar operating characteristics. Examples include: single engine; multiengine; land; water; gyroplane; helicopter; airship; and free balloon;

Elsewhere in chapter 14 of the CFR, helicopter is given as a class of the rotorcraft category, for example in §61.161

§61.161   Aeronautical experience: Rotorcraft category and helicopter
  class rating.
(a) A person who is applying for an airline transport
  pilot certificate with a rotorcraft category and helicopter class
  rating, must have at least 1,200 hours of total time as a pilot that
  includes at least:

Therefore, we see that helicopter is a class and will not have any sub–classes. Helicopter and gyrocopter are the classes of the rotorcraft category.

authors: Юрий Щепилов


text:
What is the meaning of "airport pressure altitude" on a flight performance graph?
In a flight performance graph what is the meaning of airport pressure altitude? Is it the top of climb? Because if I set my altimeter to 29.92 it will give me the pressure altitude for an airport at msl to be 0 feet, but in a performance graph I saw an airport pressure altitude to be 6000 feet.

Re " Cause if I set my altimeter to 29.92 it will give me the pressure altitude for an airport at msl to be 0 feet" -- this is not correct unless the airport is at sea level.

Pressure altitude is the altitude you see on the altimeter when it is set to 29.92.  If you take off out of Colorado Springs (6,187' FT MSL) and set 29.92 on the altimeter you won't see 0' on the altimeter, you will see something near 6,187' FT MSL
On the performance graphs, we convert the airport elevation and cruising altitude to pressure altitudes by applying the conversion between standard pressure (29.92) and actual pressure.
The formula is as follows:

29.92 - [Airport reported altimeter setting]
Multiply result by 1,000
Add result to airport elevation or cruising altitude

For example.  At Colorado Springs (6,187) and a current altimeter setting of 29.85.

29.92 - 29.85 = 0.07
0.07 x 1,000 = +70
6,187 + 70 = 6,257 FT pressure altitude

If cruising at 10,000 FT, the resulting pressure altitude to be used in the performance charts would be 10,070 FT.

Thanks .For the crusing altitude who decides ( atc or pilot)  or  is there a given range to pick from , and it's me how do I determine what altitude I should set ?

Under VFR, the pilot decides on a cruising altitude.  Odd altitudes+500 going east and even altitudes+500 going west.  You look at the performance charts to determine the altitude you want to cruise at.  The higher you go, the faster the true airspeed and ground speed.  Cruising altitude depends on distance, weather, fuel, passenger, etc.  That is why you "get the big bucks" to make the best decision.

Thanks and God bless you